The present invention relates to a new and improved construction of generator for producing pulses for metal machining by electric discharges, the generator being of the type comprising a primary or main current circuit for generating and transmitting pulse forms or shapes to a pair of electrodes.
During the machining of metals by electric discharges it has been found that the most different types of pulse forms or shapes favorably affect the desired material removable at the workpiece electrode and the undesired wear at the tool electrode. Hence, pulse generators have been developed and have become known to the art which form the pulse shapes applied to the spark gap from a number of basic shapes or forms. This forming of such pulse shapes or pulse forms is accomplished in that a number of parallel current circuits can be connected by switches with the spark gap. In each of the current circuits there is produced a basic form of shape of the pulses. Now if the switches are closed in the proper timewise sequence, then composite pulse forms or shapes appear at the spark gap. However, with these state-of-the-art generators there exists the drawback that synchronization of the operation of the switches, and thus, the timewise coordination of the individual basic form of the pulses cannot be optimumly realized. A further drawback is that for reasons of economies of the system design there can only be provided a certain number of parallel current circuits, and thus, there is extremely limited the selection of the pulse forms or shapes which are applied at the spark gap. This selection limitation no longer is capable of keeping up with the enlarged fields of application of electric discharge metal machining which increase from year to year. In other words, this means that the prior art generators are not capable of fulfilling the demands for as large as possible selection of the pulse forms or shapes. Such generators have been described in Swiss Pat. No. 382,323 (AGIE, Grauert), in the book "GENERATORI IMPULSOV" by Liwschiz, Rogazev and Otto, Publisher Energija, Moscow 1970, Chapter 9-2, and in the Russian publication "Elektrophysikalische und Electrochemische Technologie", (translated basically as "Electrophysical and Electrochemical Technology") Volume 8, Moscow, 1976, "Auswahl von Parametern Fur elektroerosive Impulse" (translated basically as "Selection of Parameters for Electro-erosion Pulses"), article by Henna and Otto. In German patent publication No. 25 47 767 there is described a generator which can produce pulse shapes of any desired type. This is accomplished in that there is produced a so-called envelope curve pair constituting a lower and upper peak for the shape of the desired work pulses. Furthermore, a voltage source is provided at the primary current circuit, this voltage source possessing such a high voltage that there can be ignited the work spark in the work gap. When such voltage is not provided then can be used an additional voltage source in a parallel arrangement. This additional voltage is superimposed upon the voltage of the primary source. Furthermore, this generator functions by using the switch arrangement taught in Swiss Pat. No. 382,323. The generator described in the aforementioned German patent publication 25 47 767 is extremely complicated, and owing to its special design and configuration and individual circuit components is associated with difficulties in realizing a practical circuit design.